1. Field of the Invention
The present invention relates to a method of controlling color lighting in a vision system, and more particularly, to a method of controlling color lighting capable of searching for a voltage value of color lighting rapidly, which allows an optimal product image to be obtained.
2. Description of the Related Art
Typically a vision system is embedded in examination equipment developed for automatically, rapidly and accurately performing various naked-eye examinations for appearance of an examination target object. The naked-eye examinations rely on human vision. The vision system plays a role of capturing and collecting digital images for the examination target object, and transferring the digital images to a processing system having a function of determining a quality of digital images.
This vision system includes a lighting device illuminating an examination target object, and a camera capturing the examination target object and creating digital images. As the camera, not an expensive color camera but a monochrome camera is mostly used.
Although the lighting device employs a predetermined monochrome lighting, nowadays, vision systems are on the increase, which employ controllable color lighting in order to effectively detect surface defects of an examination target object, like LCD appearance examination equipment disclosed in Korean Patent Application Laid-Open No. 2006-0027225.
However, since correlation between image quality and color lighting conditions for a monochrome image captured by a monochrome camera is ambiguous, an operator is required to manually find out and set optimal color lighting conditions one by one.
This scheme is not only very cumbersome, but also ambiguous, since whether the found color lighting conditions are optimal is determined according to an operator's vision and this cumbersome setting job is performed again each time an examination target object is changed.
Due to this inconvenience, when various kinds of examination target objects are to be examined, a separate vision system is embedded to each examination target object, which increases costs of the examination equipment.
Accordingly, in the case of a vision system employing color lighting, a processing system determines a quality of an examination target object through images collected by a vision system and an optimal color lighting control method is an important development target. The method maximizes image quality to allow the processing system to read images captured by a monochrome camera, and rapidly and accurately determines their quality.
In the vision system, since a large standard deviation σ of grey level I indicates that there are different contrast differences over an entire captured image, a large standard deviation value is desirable to obtain optimal images.
Meanwhile, since the grey level I varies according to a voltage V of lighting and a standard deviation σ and also varies according to a voltage of lighting, it is desirable to rapidly search for a voltage value to allow the standard deviation σ to be a maximum in order to obtain optimal images.
In the related art, as shown in FIG. 1, a scheme is used for searching for a voltage value corresponding to the largest standard deviation σ from among all standard deviations measured for a voltage value range according to each varied voltage when the voltage is continuously increased by a predetermined size.
However, in this scheme, since measurement and operations are performed for all the voltage ranges one by one, it takes a very long time. In particular, for color lighting, since a plurality of lightings is included, a more processing time is necessary.
For example, when n level voltage values are adjusted for each m lightings, nm voltage value adjustments and operations are repeated to search for optimal voltage values. Accordingly, when it is assumed that a voltage is adjusted by 0.05V in the range of 0 V to 5 V for three RGB optical sources, optimal conditions are obtained through million times voltage adjustments, which take a very long time.